The present invention relates to methods for break-in and conditioning polishing pads, specifically fixed abrasive polishing pads. The polishing pads are useful for chemical-mechanical polishing (CMP) of metal films and /or lines such as copper, tungsten, aluminum, tantalum/tantalum nitride, titanium/titanium nitride, platinum, and dielectric films and/or lines such as silicon dioxide and polymer and semiconductor substrates.
The present invention also relates to a method of determining the wear rate of a fixed abrasive polishing pad.
Semiconductor wafers having integrated circuits fabricated thereon must be polished to provide a very smooth and flat surface which in some cases may vary from a given plane by as little as a fraction of a micron. Such polishing is usually accomplished in a chemical-mechanical polishing (CMP) operation utilizing a chemically active slurry with abrasive particles that is buffed against the wafer surface by a polishing pad. A conventional polishing slurry contains appropriate chemistry and abrasive particles that facilitate the removal of materials both mechanically and chemically with a conventional pad.
Alternatively, a polishing pad containing a fixed abrasive can be used. A fixed abrasive pad incorporates the abrasives into the pad using a resin. Thus, the polishing solution accompanying this pad does not require abrasive particles. In other words, a solution comprised of appropriate chemistry in the absence of abrasives can be used to remove the materials chemically while the mechanical abrasion can be obtained from the relative motion of the pad with abrasives to the wafer in the presence of pressure.
As with most polishing pads, fixed abrasive polishing pads require break-in and conditioning to achieve consistent polishing results. Break-in and conditioning are techniques that modify the surface topography of the fixed abrasive pad to bring the pad within an optimized CMP process window. Break-in is used to prepare a fixed abrasive polishing pad for polishing. Conditioning is used after a polishing pad has been used for polishing. During the polishing process, the surface and polishing properties of polishing pads can change. The topography of the polishing pad surface can be worn down and the surface can become smooth as polishing by-products such as removed wafer material become embedded in the surface. The overall performance of the polishing pad can, consequently, deteriorate and fall out of the optimized process window. Conditioning is used to restore the polishing pad""s properties and thereby bring it back within the optimized process window.
Break-in and conditioning are both techniques aimed at affording a polishing pad with stable removal rates and better uniformity. Conditioning generally involves making passes or sweeps over the polishing surface of the pad with an abrasive material that removes a thin layer of pad material and, if present, polishing by-products. U.S. Pat. No. 5,486,131 describes an abrasive conditioning technique that is suitable for use with a conventional polyurethane polishing pad such as IC-1000 that is available from Rodel, Inc., of Newark, Del.
A new generation of fixed abrasive polishing pads is currently being developed. New generation fixed-abrasive polishing pads have a planarizing surface with exposed abrasive particles. The planarizing surface on some abrasive pads has a pattern of topographical features. One type of fixed abrasive polishing pad is described in U.S. Pat. No. 5,692,950. This polishing pad comprises a three-dimensional, textured, fixed abrasive element; at least one resilient element generally coextensive with the fixed abrasive element; and at least one rigid element generally coextensive with and interposed between the resilient element and the fixed abrasive element. Generally, the fixed abrasive element is a fixed abrasive article comprising a backing on which is disposed an abrasive coating comprising a plurality of abrasive particles dispersed in a binder in the form of a predetermined pattern.
One method of conditioning polishing pads is to abrade them with a conventional diamond-embedded abrasive disk. However, U.S. Pat. No. 5,725,417 notes that, although conventional diamond-embedded abrasive disks are well suited to condition conventional polishing pads, they are not well suited to condition the new generation fixed abrasive polishing pads. U.S. Pat. No. 5,725,417 indicates that when a fixed abrasive polishing pad is conditioned with a diamond-embedded abrasive disk, the diamonds not only remove waste material, but they also remove some of the abrasive particles and damage the topographical features on the polishing surface of the pad. Clearly such a result is not desired.
In view of this, U.S. Pat. No. 5,725,417 describes a method of conditioning a fixed abrasive polishing pad by diffusing a conditioning fluid into the suspension medium of the polishing pad in order to form a discrete stratum of material on the suspension medium that is soluble in a wash fluid. The discrete stratum is then removed by dissolving it in a wash fluid, thereby leaving a new polishing surface on the suspension medium.
Since most manufacturers already use conventional conditioning equipment, it would be useful to discover a method of break-in and conditioning using this equipment. It is, therefore, desirable to discover alternative methods of break-in and conditioning fixed abrasive polishing pads that do not damage its topographical features, use conventional equipment, and that are simple, efficient, and effective.
The present invention provides a method of break-in and conditioning a fixed abrasive polishing pad using a conditioning element, wherein the element, comprises: an upper surface and a lower conditioning surface, comprising: abrasive particles.
Also provided is a method of determining the wear rate of a fixed abrasive polishing pad without using conventional abrasive tests.